Hello I would like to add some unconditioned storage room in my attic,maybe later on down the road add on a room and a dormer. My house was built in 1948 2x4 roof rafters 24inches on center 17í7inches long, peak height is 9 foot. Ceiling joist are also 2x4. Currently there are braces from mid way through the rafter to the center of the attic no purlin. I would like to remove the braces and add a knee wall and collar ties in its place. I donít know how high the knee wall needs ton and how low the collar ties will be to support the roof. please see the attached pics and feel free to contact me for additional information
Thank You
John

Welcome to the site.
The angle braces are nailed as close the the bearing wall below because they do carry much of the load of the roof because without them the rafters are overspanned.
To take them out and add nee walls you have to be concerned about the ceiling joists, 2x6s just won't be enough. Unless you have two bearing walls the attic access framing is a little suspect too.

Wow, that could be one of the many California bungalows we have here in the historic district of Orange.
I have helped people use this space before as additional living area. Not an easy process though.
If you are in a historic district you have to design the exterior to their standards and even then you have a long way to go to make the area code compliant for living space.
You have to think about the stairs to get to the space, the emergency egress, the insulation, how to condition the space and many other things before getting to the structural aspects.
In short, you should get approvals from your planning and Building departments first.

Around here snow loading would have caused the roof to fail in 1949 so I assume you live in a warm climate and that does beg to ask where is the insulation? Starting at the roof it looks like the framing was done to support wood shingles back in the day with the spacing between the stripping. At some point the plywood was added and I’m guessing asphalt shingles of some sort. You already have a good amount of load on those 2x4 rafters. All the bracing was done making the whole thing into a type of space structure kind of a 3D truss. The ceiling joists are also 2x4 and support plank sheathing on the bottoms as structure for the ceiling below. Once again this is working as a space structure to some extent and those 2x4 on 24 centers will not support any kind of load for storage or really for living space IMHO.

Someone would need to see how much weight the outside load bearing walls can carry and how much is on them now and then a new structure would need to be built inside the original with larger rafters and floor joists if the support walls could take the loading.

I don’t think you will find a simple solution such as taking out that bracing and putting down some flooring with some short walls. You also have to deal with the air handling equipment up there.

If you were to do any type storage up there I would keep it on the very light side. It’s very easy to add some real loads one box at a time.

Bud thank for the info. Insulation was removed on this winter In preparation. I am currently having the air handler equipment moved and new duct work installed. the house is located in Houston Texas. Hopefully I'll be done before summer so I can reinsulate.

Sounds like you are proceeding. Have you talked to a builder or structural eng. about the project. It looks like the ceiling joists are overlapped in the center. Is there a loadbearing wall of any kind or beam below that.

By today’s standards what you have now I would guess is about half of what would be required for just a non-loadbearing equipment access area such as you have.

Is the only access point to the area the one hatch shown?

It’s a nice big area and I can see the reason you want to make use of it. But before I floored it and removed any of that cross bracing I would really have the numbers run. I’m sure others will have opinions to offer also.